A battery pack includes cylindrical columnar battery cells arranged at least in two rows and two columns along vertical and horizontal directions orthogonal to center axes of the battery cells. Each of the battery cells includes an electrode terminal forme...

A battery charger for charging a detachably attached battery pack by supplying an electric power from an external power source, the battery charger includes a notification unit for notifying a user of a charging operation by turning on or flickering a ligh...

A charging circuit includes a battery pack (4) provided with one or more secondary batteries (5) and a battery charger (1) for charging the secondary batteries, (5) the battery pack (4) being detachably attachable to the battery charger (1). The charging c...